The present invention relates to a method and apparatus for measuring the frequency of radiation in general, and in particular to a method and apparatus for measuring the frequency of electromagnetic radiation in the visible spectrum.
Because of the effect that a change of frequency in the visible spectrum has on a typical human eye in terms of the sensation of color, it is frequently desirable to measure the frequency of radiation from a device in the visible spectrum to determine and distinguish one color from another emitted, scattered or reflected from the device. In the fabrication of light-emitting, scattering and reflecting devices, the need for determining the frequency of the radiation emitted, scattered and/or reflected from the device may be used for controlling the fabrication of the device as well as for determining whether or not the device meets stated color specifications.
In addition to the need for measuring the frequency of visible radiation for industrial and scientific purposes, there is also a great and long-standing need for measuring the frequency of radiation in the visible spectrum being emitted, scattered or reflected from devices and surfaces used in non-scientific and non-industrial applications. For example, in the manufacture and selection of fabrics, in the purchasing of clothes, in the decorating of rooms, including the painting, wall-papering and carpeting thereof, the persons involved in these endeavors frequently are confronted with having to mix and match colors. At the present time, the methods and apparatus available for mixing and matching colors are either relatively sophisticated, complex, and require scientific trained personnel to operate them or they are very unscientific and unsophisticated and leave much to be desired.
The scientific and sophisticated methods and apparatus currently widely employed for measuring the frequency of radiation in the visible spectrum include monochrometers. Monochrometers typically employ prisms and/or gratings for separating visible radiation by color. Typically, there is provided in a monochrometer a prism or grating which is located between a light source and a narrow slit. As the prism or grating is rotated before the slit, light in narrow bands of frequency is transmitted through the slit and detected by a broad band photo-detecting apparatus. The photo-detecting apparatus measures the energy of each of the colors passing through the slit for generating an output corresponding to the spectrum of the radiation source.
In addition to monochrometers, other devices are widely used for measuring the frequency of visible radiation. For example, a series of narrow band filters and filter wheels are widely employed in certain applications for separating the radiation from a source of radiation into its various color bands.
Because of the physical structure and operating characteristics of monochrometers, narrow band filter assemblies and filter wheels heretofore known, the apparatus is relatively expensive, non-portable and requires trained scientific personnel to operate. Consequently, it is not readily available or usable by consumers or other untrained persons.
The less sophisticated methods of mixing and matching colors typically employ the use of color charts and color swatches such as the familiar paint charts often used for mixing and matching new colors with the color of existing painted or otherwise covered surfaces. The use of colored swatches of material are also used for mixing and matching colored fabrics. Needless to say, the wide variety of shades of color, tints and tones, ambient light conditions and the physical condition of the observer makes the mixing and matching of colors using color charts and/or swatches very subjective and frequently results in many mistaken and disappointing selections.
To avoid errors in mixing and matching colors, persons frequently spend an enormous amount of time making their color choices and even then their choices are subject to ambient light conditions which may vary from day to day or are subject to artificial light conditions which may vary from room to room.